A liquid crystal display (LCD) is a type of flat panel display (FPD), which shows images by the property of liquid crystal material. Comparing with other display devices, the liquid crystal display has advantages in lightweight, compactness, low driving voltage and low power consumption, and thus has already become the mainstream product in the whole consumer market. However, the liquid crystal material of the liquid crystal display cannot emit light by itself, and thus the liquid crystal display further has a backlight module which functions to provide a light with evenly brightness distribution. The backlight module mainly comprises a backlight source, a lampshade, a reflector sheet, a light guide plate (LGP), a diffusion sheet, a brightness enhancement film, an outer frame, and so on.
Generally, the backlight module can be divided into two types, i.e. the side-light type backlight module and the direct-light type backlight module, wherein the direct-light type backlight module does not include a LGP, but reflects the light upward by a lower reflector sheet and outputs it through an upper diffusion sheet. On the other hand, the side-light type backlight module includes a LGP, wherein the light is emitted into the LGP from a side surface thereof, then is reflected due to the specific reflection function of the LGP, and finally is outputted upward from its top surface.
Referring now to FIGS. 1 and 2, a side view of a traditional side-light type backlight module is illustrated in FIG. 1, and a partially enlarged view of a reflector sheet on one side of a LGP of FIG. 1 is illustrated in FIG. 2. As shown in FIG. 1, a traditional backlight module comprises a LGP 10, a light source assembly 20 and a plurality of reflector sheets 30, wherein the LGP 10 and the reflector sheets 30 are also called a LGP assembly. The LGP 10 comprises a lower surface 10a, a light input side surface 11 and a light output surface 12, wherein the lower surface 10a is opposite to the light output surface 12, and the light input side surface 11 is connected between the light output surface 12 and the lower surface 10a. The light source assembly 20 comprises a light source 21 and a lampshade 22. The light source assembly 20 is adjacent to the light input side surface 11 of the LGP 10, and the light source assembly 20 is used to provide a light to emit into the light input side surface 11 of the LGP 10. The reflector sheets 30 are disposed on other side surfaces of the LGP 10, except for the light input side surface 11. (As shown in FIG. 1, a reflector sheet 30 is disposed on a side surface of the LGP 10 opposite to the light input side surface 11.)
As shown in FIG. 1, a light beam is exemplified, wherein the light beam is reflected between the lower surface 10a and the light output surface 12 in the LGP 10, and finally reflected to a side surface the LGP 10 opposite to the light input side surface 11. If meeting conditions of total reflection, the light beam will directly go back into the LGP 10; and if not meeting the conditions of total reflection, the light beam will emit out of the LGP 10 and reflect to the reflector sheet 30. Then, the light beam will be reflected from the reflector sheet 30 and go back into the LGP 10.
Furthermore, referring to FIGS. 1 and 2, for outputting the light beam from the light output surface 12, the lower surface 10a of the LGP 10 further has dots 13 (or microstructures) to destroy the phenomenon of total reflection during outputting the light beam from the light output surface 12, wherein the light beam can carry out the diffuse reflection due to the dots 13. Thus, the light beam after the diffuse reflection does not meet the conditions of total reflection of the light output surface 12 and thus can be outputted upward from the light output surface 12 for being used as a backlight source of a liquid crystal display. A lower reflector sheet 14 is further disposed below the LGP 10, in order to guide other light beam which emits downward due to the diffuse reflection back into the LGP 10 for increasing the light utilization efficiency.
However, there is still a technical problem existing in the traditional side-light type backlight module. As shown in FIG. 2, the reflector sheet 30 is attached to the side surface of the LGP 10 by a transparent adhesive layer 31. Because the refractive index of the LGP 10 and the transparent adhesive layer 31 is equal to about 1.5. Thus, when the light beam passing through the LGP 10 and the transparent adhesive layer 31 is reflected by the reflector sheet 30, it will cause a phenomenon of diffuse reflection (due to imperfect smooth surface). As a result, a portion of light beam goes back into the LGP 10 and emit to the light output surface 12, wherein the portion of light beam can not meet the conditions of total reflection (the incident angle smaller than 42 degree) and thus directly emit out of the light output surface 12. Because the portion of light beam is not dispersed by the dots 13 (or microstructures) on the lower surface 10a, the portion of light beam is relatively bright and will cause a light leakage phenomenon at edge neighboring regions of the LGP 10, so as to affect the total display effect.
In the traditional technology, to solve the foregoing problem, the width of an outer frame of a display may be further increased. The outer frame 40 as shown by imaginary lines in FIG. 2 has a width, wherein the width of the outer frame 40 is designed to shade a maximum region of the LGP 10 where may generate the light leakage (L). However, this solution can not essentially solve the generation of the light leakage phenomenon. Thus, for satisfying needs of efficient visual angle of liquid crystal displays, the LGP 10 must add its area (i.e. add material), resulting in lowering the light utilization efficiency. Moreover, the profile of the display must be widened, but it will be disadvantageous to carry out the design of narrow frame edges.
As a result, it is necessary to provide a side-light type LGP assembly and backlight module to solve the problems existing in the conventional technologies, as described above.